As used herein, the term "rotary extruder" refers to an extruder having a barrel section with an eccentric bore and a rotor that comprises a substantially cylindrical plasticizing surface rotatably mounted within the bore. Polymeric resin, typically in the form of pellets, flakes or powder, is introduced into a clearance zone between the rotor and the interior surface of the barrel through a feed port. The resin is then plasticized and delivered to a discharge port as the rotor rotates within the stationary barrel. Extruders of this general type, which differ substantially from conventional rotating screw extruders, have previously been disclosed, for example, in U.S. Pat. Nos. 3,880,564; 4,012,477; 4,501,543; and 4,813,863.
Rotary extruders utilize bearings near each end of the rotor to reduce friction and the power required to rotate the rotor within the barrel. In the past, these bearing have been cooled by circulating water through the bearing housings. It is now believed that the operating temperature of the bearings can be reduced and bearing life increased by providing internal cooling to that section of the rotor with which the bearings make contact. In so doing, however, care must be taken to minimize any associated cooling of that portion of the rotor where polymeric resin is being plasticized.
Although the use of water cooling inside the feed section of a conventional extruder screw has been disclosed in U.S. Pat. No. 3,482,006 for the purpose of preventing additives from melting prematurely during the manufacture of thermoplastic foam, the teachings of that reference are contrary to the goal of not significantly reducing the temperature of the rotor surface adjacent to the feed zone.
Apparatus is therefore needed that will achieve the above-stated objectives within a rotary extruder.